1. Field of the Invention
The present invention relates to a position control method for an elevator, and in particular to a position control method for an elevator by which the cage of an elevator can arrive at a desired floor by computing a speed pattern of a cage before the elevator is operated and controlling the position of the cage which is operated in accordance with the computed speed pattern, and which is capable of judging the position of the cage based on the pulse from a position detector, and changing the speed pattern based on an error when the error occurs between the judged position of the cage and the position of the cage which was previously set, so that the cage is more accurately operated based on the changed speed pattern.
2. Description of the Conventional Art
FIG. 1 is a view illustrating the construction of a conventional elevator position control apparatus.
As shown therein, the conventional position control apparatus for an elevator includes a cage 2, a position detector 3 having a permanent magnet 31 and a reed switch 32 and disposed in an upper portion of the cage 2 for outputting a position detection signal in cooperation with a shield plate 4 disposed in a side wall of a cage moving path 1, a motor 9, an encoder 10 for outputting a pulse corresponding to the number of rotations of the motor 9, an operation controller 6 for judging the position of the cage 2 based on the position detection signal from the position detector 3 and the output signal from the encoder 10 when a floor call is requested from the cage 2 and for outputting a speed command signal v* so as to move the cage 2 to a service floor, a motor controller 7 for outputting a control signal cs for controlling the speed of the motor 9 in accordance with the speed command signal v* inputted thereto, and an inverter 8 for receiving the control signal cs and for outputting a phase voltage to the motor 9.
When the height of the bottom of the cage 2 is the same as the bottom of the floor 5, the position detector 3 disposed in the upper portion of the cage 2 is positioned at the center portion of the shield plate 4. Therefore, as the cage 2 is moved, when the position detector 3 passes through the shield plate 4, a magnetic force from the permanent magnet 31 is blocked by the shield plate 4, and then the reed switch 32 is turned off.
The position control process of the conventional position detection apparatus for an elevator will now be explained with reference to the accompanying drawings.
Before the elevator is normally operated, the operation controller 6 operates the cage 2 from the lowest floor to the highest floor so as to set a floor height value of each floor. Here, the lowest floor is assumed as a first floor.
When the cage 2 is operated from the first floor, the encoder 10 outputs a pulse corresponding to the number of rotations of the motor 9, and output pulse is inputted to the operation controller 6, and a direct current voltage Vdc is supplied to the operation controller 6 through the reed switch 32 of the position detector 3.
When the cage passes through the second floor, the magnetic force from the permanent magnet 31 is blocked by the shield plate 4, and then the reed switch 32 is turned off, whereby the supply of the direct current voltage Vdc to the operation controller 6 is stopped. The operation controller 6 accumulates the number of pulses from the encoder 10, and sums the number of pulses from the encoder 10, which number corresponds to a length of 125 mm which is half of the length of the shield plate 4, and summed value is stored as a floor height value corresponding to the height between the first floor and the second floor. The above-described processes are repeated during the operation of the cage 2 from the highest floor to the lowest floor, for thus storing the floor height value of each floor.
After the floor height value is stored, when a user (passenger) registers the service floor at the floor 1 or in the cage 2, the operation controller 6 computes the distance from the current floor to the service floor, namely, the distance "disti" within which the cage 2 is operated. EQU dist=Pd-Po (1)
where Po denotes a floor height value of the current floor, and Pd denotes a floor height value of the service floor.
Next, the operation controller 6 determines the speed pattern from the distance "dist" within which the cage 2 is operated. The speed pattern will now be explained with reference to FIGS. 2 through 3D.
FIG. 2 is a graph of the acceleration based on a running time of an elevator in the conventional art. As shown therein, there are seven intervals PS1 through PS7 in accordance with the pattern of the acceleration. Here, PS1 and PS5 are referred to intervals within which the acceleration is increased. PS2 and PS6 are referred to intervals within which the acceleration is constant. PS3 and PS7 are referred to intervals within which the acceleration is reduced. PS4 is referred to an interval within which the acceleration is zero. In addition, J1, J2, J3, and J4 are referred as a jerk (the rate of change of acceleration).
The speed of each interval is as follows: EQU V.sub.1 (kT)=1/2(kT).sup.2 EQU V.sub.2 (kT)=J(k.sub.1 T)(kT)+V.sub.1 (k.sub.1 T) EQU V.sub.3 (kT)=-J/2(kT).sup.2 +J(k.sub.1 T)(kT)+V.sub.2 (k.sub.2 T) EQU V.sub.4 (kT)=V.sub.3 (k.sub.1 T) EQU V.sub.5 (kT)=-1/2(kT).sup.2 +V.sub.4 (k.sub.4 T) EQU V.sub.6 (kT)=-J(k.sub.1 T)(kT)+V.sub.5 (k.sub.1 T) EQU V.sub.7 (kT)=1/2(kT).sup.2 -J(k.sub.1 T)(kT)+V.sub.6 (k.sub.2 T)
The distance P.sub.i (kT) of each interval can be obtained by integrating the speed of each interval with respect to time as follows: EQU P.sub.i (kT)=.intg.V.sub.i dt, i=1, 2, . . . , 7 (3) EQU P.sub.7 (T.sub.1)dist+Po
Therefore, the total distance "dist" within which the cage 2 is operated is obtained as follows from the distance P.sub.i (kT). EQU dist=2J(k.sub.1 T).sup.3 +3J(k.sub.1 T).sup.2 (k.sub.2 T)+J(k.sub.1 T).sup.2 (k.sub.4 T)+J(k.sub.1 T)(k.sub.2 T).sup.2 +J(k.sub.1 T)( k.sub.2 T)(k.sub.4 T) (4)
The speed pattern of each interval is determined based on Equation (4). In addition, since the acceleration "J" and the intervals (SP1, SP3, SP5, and SP7) within which the acceleration is varied are previously set, the unknown values are k.sub.2 T and k.sub.4 T.
Therefore, so as to solve the unknown values, four different acceleration patterns are used as shown in FIG. 3.
FIG. 3a illustrates the acceleration pattern when the distance of the intervals SP2, SP4, and SP6 are zero (0), respectively, and Dref1 denotes the minimum distance within which the cage can be operated. FIG. 3B illustrates the acceleration pattern when the distance of the interval SP4 is zero (0), and FIG. 3C illustrates the acceleration pattern when the distance of the interval SP4 is zero (0), and when the cage 2 reaches the rated speed, and FIG. 3D illustrates the acceleration pattern when the cage 2 is operated at the rated speed, and when the interval SP4 is variable. In addition, as shown in FIGS. 3C and 3D, the area "b" is as the rated speed, and "a" denotes the distance when the cage reaches at the rated speed.
Here, since the intervals SP2, SP4, and SP6 are zero (0), the distance Dref.sub.1 is as follows. EQU D.sub.ref1 =2J(k.sub.1 T).sup.3 ( 5)
Since the area "b" is the rated speed, and the interval SP4 is zero (0), the distance Dref2 can be obtained by the following equation. Here, A.sub.MAX denotes the maximum value of the acceleration. EQU V.sub.REF =(k.sub.1 T+k.sub.2 T)A.sub.MAX EQU k.sub.2 T=V.sub.REF /A.sub.MAX -k.sub.1 T EQU A.sub.MAX =J(k.sub.1 T) EQU D.sub.ref2 =J(k.sub.1 T)2(k.sub.1 T).sup.2 +3(k.sub.1 T)(k.sub.2 T)+(k.sub.2 T).sup.2 ! (6)
The operation controller 6 judges the appropriate accelation pattern at which the cage 2 is being operated from the four acceleration patterns. This process will now be explained with reference on FIG. 4.
If the distance "dist" within which the cage 2 is operated is shorter than the minimum distance Dref1 in step S41, it is judged that the system has a predetermined error.
In addition, if the distance "dist" within which the cage 2 is operated is longer than the distance Dref1, and shorter than the distance Dref2 in step S42, the pattern with which the cage 2 is operated is shown in FIG. 3B. In this case, since k.sub.4 T is zero (0) in accordance with Equation 4, the value of k.sub.2 T is computed in step S43.
In addition, if the distance "dist" within which the cage 2 is operated is longer than the distance Dref2, and when the speed of the cage 2 reaches the rated speed of V.sub.REF, the value of k.sub.2 T is the same as the value computed based on Equation (6) in step S44, and the value of k.sub.4 T is computed by substituting the computed value k.sub.2 T into Equation 4 in step S45.
When the speed pattern with which the cage 2 is operated is determined, the position P.sub.i (kT) of the cage 2 within each interval PSi is computed based on Equation 4 in step S46.
The position P.sub.i (kT) of the cage 2 is stored as a reference position Pr, and then the cage 2 is in a ready mode for operation.
The operation controller 6 outputs a speed command signal v* in accordance with the determined speed pattern, and then the motor 9 is driven so as to drive the cage 2. The pulse from the encoder 10 which pulse corresponds to the number of the rotation of the motor 9 is inputted to the operation controller 6.
The operation controller 6 detects the current position of the cage 2, namely, a synchronous position Pc, in accordance with the pulse inputted thereto, compares the synchronous position Pc with the reference position Pr, computes a position difference OFFSET, and outputs the value obtained by multiplying the position difference OFFSET by a predetermined gain GAIN as a new speed command signal v*. EQU v*=GAIN*OFFSET (7)
As described above, during the operation of the cage 2, the number of pulses from the encoder 10 may be different from the number of pulses counted by the operation controller 6 due to an unknown cause occurred in the system. In addition, when a rope connecting the cage 2 and a counterweight 11 may be elongated, for thus causing a slippage between a sheave and the rope, there may be an error between the position of the cage 2 which is judged based on the output pulse from the encoder 10 and the actual position of the cage 2. In this case, the cage can not accurately arrive at the service floor.
Therefore, so as to overcome the above-described problems, the synchronous position is corrected by using a device such as a position detector.
However, in the conventional position control method of outputting the position error corrected the synchronous position, when the position difference OFFSET is large, since the speed command signal may be significantly change, the motor which is driven in accordance with the speed command signal may be overloaded, thus causing a malfunction of the system.
Namely, as shown in FIGS. 3C and 3D, the maximum value of the rated speed is set as "a". However, when the speed is increased within the intervals SP1, SP2, and SP3 as shown in FIGS. 3C and 3D, the cage 2 is operated at over rated speed "a", and thus causing the malfunction of the motor.
In addition, when the speed command signal is changed within the intervals SP1, SP2, SP5, and SP7 within which the acceleration is changed, the speed pattern becomes discontinuous, and thus causing the system to be unstable, and the ride of the cage 2 is bad.
Moreover, the cage may not accurately arrive at the service floor due to overloading of the system.